Set retarder compositions, cement compositions, and associated methods

ABSTRACT

Cement compositions, that comprise water, a cement, a strength-retrogression additive, and an acid, wherein the acid comprises ethylenediamine tetra acetic acid, nitrilotriacetic acid, or a combination thereof, are provided. Methods of cementing in a subterranean formation, methods of retarding the set time of a cement composition, and set retarder compositions also are provided.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention is a divisional of U.S. application Ser. No.10/963,035 entitled “Set Retarder Compositions, Cement Compositions, andAssociated Methods” filed on Oct. 11, 2004, the entire disclosure ofwhich is incorporated herein by reference.

BACKGROUND

The present invention relates to cementing operations, and moreparticularly, to set retarder compositions that comprise ethylenediaminetetra acetic acid and/or nitrilotriacetic acid, cement compositions thatcomprise the set retarder compositions, and associated methods.

Cement compositions are commonly utilized in subterranean operations,particularly subterranean well completion and remedial operations. Forexample, cement compositions are used in primary cementing operationswhereby pipe strings such as casings and liners are cemented in wellbores. In performing primary cementing, cement compositions are pumpedinto the annular space between the walls of a well bore and the exteriorsurface of a pipe string disposed therein. The cement composition ispermitted to set in the annular space, thereby forming an annular sheathof hardened substantially impermeable cement therein that supports andpositions the pipe string in the well bore and bonds the exteriorsurface of the pipe string to the walls of the well bore. Cementcompositions also are used in remedial cementing operations such asplugging highly permeable zones or fractures in well bores, pluggingcracks and holes in pipe strings, and the like.

These cementing operations generally occur under a wide variety of wellbore conditions, for example, ranging from shallow wells (less thanabout 1,000 feet) to extremely deep wells (greater than about 35,000feet). Generally, the cement composition should remain in a pumpablestate until the cement composition has been placed into the desiredlocation. To retard the set time of the cement composition, conventionalset retarder compositions have been included therein. As used herein,the phrase “conventional set retarder compositions” refers to a widevariety of compositions commonly used in cementing operations fordelaying the set time of a cement composition, including lignosulfates,hydroxycarboxy acids, phosphonic acid derivatives, synthetic polymers(e.g., copolymers of 2-acrylamido-2-methylpropane sulfonic acid(“AMPS”)), borate salts, and combinations thereof. As used herein, theterm “copolymer” refers to a polymer comprising two or more differentmonomers. Certain of these conventional set retarder compositions (e.g.,synthetic polymers) may be costly to produce, which may add an undesiredexpense to the cementing operation. Further as temperatures encountereddownhole increase, higher concentrations of the conventional setretarder compositions may be required to achieve a desirable level ofset retardation, which, in turn, may lead to additional undesiredexpense to the cement operation. Even further, these conventional setretarder compositions may not provide a desired level of setretardation, for example, in wells having bottom hole circulatingtemperatures (“BHCT”) above about 450° F. Therefore, these temperatureslimit the temperatures at which a cement composition may be pumped usingconventional set retarder compositions and, thus, limit the depths andassociated temperatures at which well bores may be drilled and isolatedwith a cement composition placed in the annulus.

SUMMARY

The present invention relates to cementing operations, and moreparticularly, to set retarder compositions that comprise ethylenediaminetetra acetic acid and/or nitrilotriacetic acid, cement compositions thatcomprise the set retarder compositions, and associated methods.

In one embodiment, the present invention provides a method of cementingin a subterranean formation penetrated by a well bore that comprisesproviding a cement composition comprising water, a cement, astrength-retrogression additive, and an acid, wherein the acid comprisesethylenediamine tetra acetic acid, nitrilotriacetic acid, or acombination thereof; introducing the cement composition into thesubterranean formation; and allowing the cement composition to settherein.

In another embodiment, the present invention provides a method ofretarding the set time of a cement composition that comprises adding tothe cement composition an acid, wherein the acid comprisesethylenediamine tetra acetic acid, nitrilotriacetic acid, or acombination thereof.

In another embodiment, the present invention provides a cementcomposition that comprises water, a cement, a strength-retrogressionadditive, an acid, wherein the acid comprises ethylenediamine tetraacetic acid, nitrilotriacetic acid, or a combination thereof.

In yet another embodiment, the present invention provides a set retardercomposition that comprises an acid, wherein the acid comprisesethylenediamine tetra acetic acid, nitrilotriacetic acid, or acombination thereof.

The objects, features and advantages of the present invention will bereadily apparent to those skilled in the art upon a reading of thedescription of the specific embodiments that follows.

DESCRIPTION

The present invention relates to cementing operations, and moreparticularly, to set retarder compositions that comprise ethylenediaminetetra acetic acid and/or nitrilotriacetic acid, cement compositions thatcomprise the set retarder compositions, and associated methods. Whilethe methods and compositions of the present invention may be useful in avariety of subterranean cementing operations, they are particularlyuseful for cementing operations in well bores having BHCTs greater thanabout 450° F., among other things, due to desirable properties (e.g.,placement time) of the cement compositions of the present invention.

The cement compositions of the present invention generally comprisewater, a cement, a strength-retrogression additive, and an acid, whereinthe acid comprises ethylenediamine tetra acetic acid (“EDTA”),nitrilotriacetic acid (“NTA”), or a combination thereof. In someembodiments, the cement compositions of the present invention furthermay comprise a conventional set retarder composition and/or a copolymerthat comprises olefinically unsaturated non-acrylate sulfonate (“OUS”)monomers and olefinically unsaturated carboxylic acid (“OUC”) monomers(e.g., styrene sulfonic acid and maleic anhydride). As used herein, thephrase “strength-retrogression additive” refers to materials (e.g.,crystalline silica) that are capable of preventing the strengthretrogression of a set cement composition when exposed to hightemperatures. Generally, the cement compositions of the presentinvention should be useful in cementing operations in well bores havinga BHCT of up to about 700° F. In some embodiments, the cementcompositions of the present invention may be used in well bores wheresome delay in the set time of the cement composition is desired, forexample, in well bores having a BHCT of greater than about 200° F. Insome embodiments, the cement compositions of the present invention maybe used in well bores having a BHCT in the range of from about 450° F.to about 700° F. The inclusion of copolymers comprising OUS monomers andOUC monomers in the cement compositions of the present invention mayprovide desirable levels of set retardation in well bores having BHCTsabove about 525° F.

Generally, the cement compositions of the present invention may have adensity suitable for a particular application. In one embodiment, thecement compositions of the present invention may range in density fromabout 12 pounds per gallon (“ppg”) to about 30 ppg. In yet anotherembodiment, the cement compositions of the present invention may rangein density from about 17 ppg to about 21 ppg.

Suitable water for use in the cement compositions of the presentinvention includes fresh water, saltwater (e.g., water containing one ormore salts dissolved therein), brine (e.g., saturated saltwater), orseawater. Generally, the water may be from any source provided that itdoes not contain an excess of compounds that adversely affect the cementcompositions. The water maybe present in an amount sufficient to form apumpable slurry. Generally, the water is present in the cementcompositions of the present invention in an amount in the range of fromabout 33% to about 200% by weight of cement (“bwoc”) therein. In certainembodiments, the water is present in the cement compositions of thepresent invention in an amount in the range of from about 35% to about60% bwoc therein.

Any cements suitable for use in subterranean applications are suitablefor use in the present invention. In one embodiment, the improved cementcompositions of the present invention comprise a hydraulic cement. Avariety of hydraulic cements are suitable for use including thosecomprised of calcium, aluminum, silicon, oxygen, and/or sulfur, whichset and harden by reaction with water. Such hydraulic cements include,but are not limited to, Portland cements, pozzolanic cements, gypsumcements, high alumina content cements, silica cements, combinationsthereof, and the like.

Any strength-retrogression additive suitable for use in subterraneanapplications may be included in the cement compositions of the presentinvention. Strength retrogression agents generally are included in thecement composition of the present invention, among other things, toprevent high-temperature strength retrogression that occurs to setcement compositions in high-temperature wells, for example, wells with aBHCT that exceeds about 230° F. Examples of suitablestrength-retrogression additives include crystalline silica, such as,e.g., coarse grain crystalline silica, fine grain crystalline silica, ora combination thereof. An example of a suitable fine grain crystallinesilica is “SSA-1” strength stabilization agent, commercially availablefrom Halliburton Energy Services, Inc., Duncan, Okla. An example of asuitable course grain crystalline silica is “SSA-2” strengthstabilization agent, commercially available from Halliburton EnergyServices, Inc., Duncan, Okla. Generally, a strength-retrogressionadditive may be included in the cement compositions of the presentinvention in an amount sufficient to provide the desired level ofstrength retrogression prevention. In some embodiments, astrength-retrogression additive may be included in the cementcompositions of the present invention in an amount in the range of fromabout 30% to about 80% bwoc. Those of ordinary skill in the art, withthe benefit of this disclosure, will be able to select the appropriatetype and amount of the strength regression additive to include in thecement compositions of the present invention for a particularapplication.

The conventional set retarder composition that may be included in thecement compositions of the present invention may include anyconventional set retarder composition suitable for use in subterraneanoperations. Conventional set retarder compositions are generallyincluded in the cement compositions of the present invention to retardthe set time thereof. Examples of suitable conventional set retardercompositions include lignosulfates (“LS”), hydroxycarboxy acids,phosphonic acid derivatives, borate salts, synthetic polymers, andcombinations thereof. Examples of suitable hydroxycarboxy acids includetartaric acid, gluconic acid, citric acid, gluconoheptanoic acid,combinations thereof, and the like. An example of a suitablehydroxycarboxy acid is commercially available as “HR®-25” retarder fromHalliburton Energy Services, Inc., Duncan, Okla. Suitable syntheticpolymers include a wide variety of synthetic polymers that may be usedto delay the set time of a cement composition in cementing operations,including copolymers comprising an AMPS monomer and at least one monomerchosen from acrylic acid, methacaylic acid, itaconic acid, or maleicacid. Examples of suitable synthetic polymers are commercially availableas “SCR™-100” retarder from Halliburton Energy Services, Inc., Duncan,Okla., which is described in U.S. Pat. Nos. 4,941,536; 5,049,288;5,472,051, the relevant disclosures of which are incorporated herein byreference, and as “SCR™-500” retarder from Halliburton Energy Services,Inc., Duncan, Okla., which is described in U.S. Pat. No. 5,536,311, therelevant disclosure of which is incorporated herein by reference. Insome embodiments, the conventional set retarder composition comprisesborate salts. Examples of suitable borate salts include potassiumpentaborate, sodium tetraborate, borax, combinations thereof, and thelike. An example of a suitable borate salt is commercially available as“COMPONENT R™” additive from Halliburton Energy Services, Inc., Duncan,Okla. An example of a conventional set retarder composition comprising aphosphonic acid derivative is commercially available as “Micro Matrix™”cement retarder from Halliburton Energy Services, Inc., Duncan, Okla.,which is described in U.S. Pat. Nos. 5,340,397 and 5,484,478, therelevant disclosures of which are incorporated herein by reference. Insome embodiments, the conventional set retarder composition comprisescombinations of the above-listed compositions. An example of a suitablecombination is a conventional set retarder composition that comprisescalcium LS and gluconic acid, an example of which is commerciallyavailable as “HR-12™” retarder, from Halliburton Energy Services, Inc.,Duncan, Okla., in a 75:25 calcium LS to gluconic acid weight ratio. Oneof ordinary skill in the art will be able to determine other suitableconventional set retarder compositions that may be used in the cementcompositions of the present invention.

The amount of a particular conventional set retarder composition toinclude generally depends on a number of factors, including the BHCT andbottom hole pressure of the well bore, the particular conventional setretarder composition chosen, the cement composition of the presentinvention containing the conventional set retarder composition, andother factors known to those of ordinary skill in the art. As those ofordinary skill in the art, with the benefit of this disclosure, willappreciate higher concentrations of the conventional set retardercomposition may be needed with increasing BHCT. In some embodiments, thequantity of the conventional set retarder composition to be included ina cement composition of the present invention may be determined prior topreparation of the cement composition. For example, the quantity of aconventional set retarder composition to be included in a cementcomposition of the present invention may be determined by performingthickening time tests of the type described in API Recommended Practices10B, Procedure 9, Twenty-Second Edition, December 1997. Moreparticularly, in certain embodiments, a conventional set retardercomposition is present in the cement compositions of the presentinvention in an amount in the range of from about 0.01% to about 10%bwoc. In some embodiments, a conventional set retarder composition ispresent in the cement compositions of the present invention in an amountin the range of from about 0.1% to about 6% bwoc.

The cement compositions of the present invention further comprise EDTAand/or NTA. Among other things, EDTA and/or NTA may be included in thecement compositions of the present invention so the cement compositionsmay have desirable levels of set retardation, for example, in well boreshaving a BHCT of greater than about 450° F. Further, inclusion of EDTAand/or NTA may reduce the amount of a conventional set retardercomposition that may be needed to achieve a desired level of setretardation, thereby possibly reducing the expense associated with thecementing operation, for example, where a synthetic polymer is includedin the conventional set retarder composition.

Generally, the EDTA and/or NTA should be included in the cementcompositions of the present invention in an amount sufficient to providethe desired level of set retardation in the cement compositions of thepresent invention, based on a number of factors including the amount andcomposition of the convention set retarder compositions, desiredplacement time, and the BHCT and bottom hole pressure of the well bore.As those of ordinary skill in the art, with the benefit of thisdisclosure, will appreciate higher concentrations of the conventionalEDTA and/or NTA may be needed with increasing BHCT. In some embodiments,the quantity of the EDTA and/or NTA to be included in a cementcomposition of the present invention may be determined prior topreparation of the cement composition. For example, the quantity of aconventional set retarder composition to be included in a cementcomposition of the present invention may be determined by performingthickening time tests of the type described in API Recommended Practices10B, Procedure 9, Twenty-Second Edition, December 1997. In someembodiments, the EDTA may be present in the cement compositions of thepresent invention in an amount in the range of from about 0.01% to about10% bwoc. In some embodiments, the EDTA may be present in the cementcompositions of the present invention in an amount in the range of fromabout 0.01% to about 6% bwoc. In some embodiments, the NTA may bepresent in the cement compositions of the present invention in an amountin the range of from about 0.01% to about 10% bwoc. In some embodiments,the NTA may be present in the cement compositions of the presentinvention in an amount in the range of from about 0.01% to about 6%bwoc. In some embodiments, where used in combination, the EDTA and theNTA may be present in the cement compositions of the present inventionin an amount in the range of from about 0.01% to about 10% bwoc. In someembodiments, where used in combination, the EDTA and NTA may be presentin the cement compositions of the present invention in an amount in therange of from about 0.01% to about 6% bwoc. Generally, where used incombination, the ratio of the EDTA to the NTA may vary based on a numberof factors including, the desired set time, desired placement time,BHCT, and a variety of other factors known to those of ordinary skill inthe art. In some embodiments, the ratio of the EDTA to the NTA may be inthe range of from about 1:5 by weight to about 5:1 to weight. In someembodiments, the ratio of the EDTA to the NTA may be in the range offrom about 1:2 by weight to about 2:1 to weight.

The cement compositions of the present invention optionally may comprisea copolymer that comprises OUS monomers and OUC monomers. Inclusion ofthese copolymers in the cement compositions of the present invention,among other things, may provide desirable levels of set retardation inwell bores having BHCTs over about 525° F. A specific example of asuitable copolymer that comprises OUS monomers and OUC monomers is astyrene sulfonic acid and maleic anhydride (“SSMA”) copolymer. Anexample of a suitable SSMA copolymer having a styrene monomer to maleicanhydride mole ratio of about 1:1 is commercially available as “NARLEX®D-72” polymer. In another embodiment, aqueous solutions of the abovepolymers containing up to about 50% polymer by weight are used. Further,numerous salts of the copolymer may be made by methods well known in theart. As used herein, the term “copolymer” is intended to include theacid form of the copolymer as well as its various salts.

The OUS monomers suitable for use in the present invention includesulfonated monomers that do not contain base-degradable functionalgroups, for example amides or esters. Examples of suitable OUS monomersinclude sulfonated styrene, vinyltoluenesulfonic acid,vinylnapthalenesulfonic acid, allyloxylbenzenesulfonic acid,3-allyloxy-2-hydroxypropane sulfonic acid, and allylsulfonic acid. Thesemonomers may used in the acid or salt form. In some embodiments, whenthe monomers are used in the acid form, the final copolymer may beneutralized prior to use.

As used herein, an OUC monomer is intended to include aliphatic,branched or cyclic, mono-, di-, or tri-carboxylic acids, the alkali oralkaline earth metal salts thereof, and the amides, esters, imides andanhydrides thereof. Suitable OUC monomers should be copolymerizable withan OUS monomer. Examples of suitable OUC monomers include acrylic acid,alkyl acrylic acids, for example methacrylic acid and ethacrylic acid;alpha-chloro-acrylic acid, alpha-cyano acrylic acid,alpha-chloro-methacrylic acid, alpha-cyano methacrylic acid, crotonicacid, alpha-phenyl acrylic acid, beta-acryloxy propionic acid, sorbicacid, alpha-chloro sorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid, beta-styryl acrylic acid (1-carboxy-4-phenylbutadiene-1,3), itaconic acid, maleic acid, citraconic acid, mesaconicacid, glutaconic acid, aconitic acid, fumaric acid, and tricarboxyethylene. Of these, maleic acid; maleimide; diesters, monoester, andamide derivatives of maleic acid; unsubstituted acrylic acid andderivatives thereof; and alkyl acrylic acid and derivatives thereof arepreferred.

The ratio of the OUS monomers to the OUC monomers in the copolymer mayvary dependent on a number of factors, including the particular monomerschosen and the desired level of set retardation. In some embodiments,the mole ratio of the OUS monomers to OUC monomers may be in the rangeof from about 100:1 to about 1:100. In some embodiments, the mole ratioof the OUS monomers to OUC monomers may be in the range of from about3:1 to about 1:3. In some embodiments, the mole ratio of the OUSmonomers to OUC monomers may be about 1:1.

Generally, the copolymer that comprises OUS monomers and OUC monomersshould be included in the cement compositions of the present inventionin an amount sufficient to provide a desired level of set retardation.In some embodiments, the copolymer that comprises OUS monomers and OUCmonomers is included in the cement compositions of the present inventionin an amount in the range of from about 0.01% bwoc to about 10% bwoc. Insome embodiments, the copolymer that comprises OUS monomers and OUCmonomer is included in the cement compositions of the present inventionin an amount in the range of from about 0.01% bwoc to about 6% bwoc.

Optionally, the cement compositions of the present invention further maycomprise a dispersant. Where present, the dispersant acts, among otherthings, to control the rheology of the cement composition. While avariety of dispersants known to those skilled in the art may be used inaccordance with the present invention, a suitable dispersant comprises awater-soluble polymer prepared by the condensation of formaldehyde withacetone and sodium bisulfite. Such a dispersant is commerciallyavailable as “CFR™-3” dispersant from Halliburton Energy Services, Inc.,Duncan, Okla. Another suitable dispersant comprises a sodium salt ofnaphthalene sulfonic acid condensed with formaldehyde, an example ofwhich is commercially available as “CFR™-2” dispersant also fromHalliburton Energy Services, Inc., Duncan, Okla. Another suitabledispersant comprises gluconic acid, an example of which is commerciallyavailable as “CFR™-1” dispersant also from Halliburton Energy Services,Inc., Duncan, Okla. Where used, the dispersant should be present in thecement compositions of the present invention in an amount sufficient toimprove the rheology of the cement composition. In some embodiments, thedispersant is present in the cement compositions of the presentinvention in an amount in the range of from about 0.1% to about 5% bwoc.In some embodiments, the dispersant is present in the cementcompositions of the present invention in an amount in the range of fromabout 0.1% to about 3% bwoc.

As will be recognized by those skilled in the art, the cementcompositions of this invention also may include additional suitableadditives, such as, for example, defoamers, fibers, fluid loss controladditives, weighting materials, salts, vitrified shale, fly ash,combinations thereof, and the like. Weighting materials may be includedin the cement compositions of the present invention to provide a desireddensity. Examples of suitable weighting materials include iron oxidesand oxides of manganese. An example of a suitable weighting materialcomprising oxide of manganese is commercially available as “MICROMAX®”from Elkem Materials, Inc., Pittsburgh, Pa. An example of a suitableweighting material comprising iron oxide is commercially available as“Hi-Dense® No. 4” cement weighting additive from Halliburton EnergyServices, Inc., Duncan, Okla. One of ordinary skill in the art with thebenefit of this disclosure will be able to recognize where a particularadditive is suitable for a particular application.

The cement compositions of the present invention may be prepared usingany suitable technique for the preparation of cement compositions. Insome embodiments, the EDTA and/or NTA may be dry blended with the cementtogether with other additives (e.g., the conventional set retardercomposition, the copolymer comprising OUS monomers and OUC monomers, andthe like). In other embodiments, salts of EDTA and/or NTA may be addedto the water used to make the cement composition. In yet otherembodiments, the EDTA and/or NTA may be dry blended with the silica andthen combined with the cement by any suitable technique. One of ordinaryskill in the art, with the benefit of this disclosure, will be able toprepare a cement composition suitable for use in a particularapplication.

In one embodiment, the present invention provides a method of cementingin a subterranean formation penetrated by a well bore that comprisesproviding a cement composition comprising water, a cement, astrength-retrogression additive, and an acid, wherein the acid comprisesEDTA, NTA, or a combination thereof; introducing the cement compositioninto the subterranean formation; and allowing the cement composition toset therein.

In another embodiment, the present invention provides a method retardingthe set time of a cement composition that comprises adding to the cementcomposition an acid, wherein the acid comprises EDTA, NTA, or acombination thereof.

In another embodiment, the present invention provides a cementcomposition that comprises water, a cement, a strength-retrogressionadditive, an acid, wherein the acid comprises EDTA, NTA, or acombination thereof.

In yet another embodiment, the present invention provides a set retardercomposition that comprises an acid, wherein the acid comprises EDTA,NTA, or a combination thereof. In some embodiments, the set retardercomposition may further comprise a copolymer that comprises OUS monomersand OUC monomers.

To facilitate a better understanding of the present invention, thefollowing illustrative example of some of the certain embodiments aregiven. In no way should such example be read to limit, or define, thescope of the invention.

EXAMPLE

Sample compositions were prepared according to the following procedure.Each sample was dry blended, then blended with water for 15 seconds at4,000 rpm in a Waring Blendor, and then mixed for 35 seconds at 12,000rpm in the Waring Blendor. After sample preparation, thickening timetests were performed on each of the samples using aHigh-Temperature/High-Pressure consistometer according to APIRecommended Practices 10B, Procedure 9, Twenty-Second Edition, December1997. While the thickening time test was being performed, each samplecomposition was brought up to T_(Test) and 32,000 psi, unless otherwisenoted, in the time listed in the tables below.

For each of Test Nos. 1-3, a summary of the sample composition andthickening times at T_(Test) between 500° F. and 545° F. is providedbelow in Table 1. The sample compositions utilized in Test Nos. 1-3 arecomparative cement compositions that comprise a conventional setretarder composition. TABLE 1 500° F. to 545° F. Tests TEST NO. Test No.1 Test No. 2 Test No. 3 Class H Cement (lbs/sack) 94 94 94 % SSA-1 bwoc10 10 10 % SSA-2 bwoc 30 30 30 Hi-Dense ® No. 4 lbs/sk 65 0 0 MicroMax ®lbs/sk 0 100 75 % NaCl bwow 18 18 18 % SCR ™-500 bwoc 5 5 5 % HR ®-25bwoc 5 5 5 % CFR ™-1 bwoc 0 5 0 % Gasstop ™ HT¹ bwoc 0.8 0 0.8 %EZ-FLO ™¹ bwoc 0.07 0.07 0.07 Water (gal/sack) 6.16 7.46 6.51 Density(lb/gal) 19 19 19 Yield (ft³/sack) 1.88 2.25 1.98 Minutes to T_(Test) 9090 90 T_(Test) (° F.) 500 500 545 Thickening Time (hr:min) 6:38 1:381:51¹Gasstop ™ HT cement additive is a gas migration and fluid loss controladditive that is commercially available from Halliburton EnergyServices, Inc., Duncan, Oklahoma.²EZ-FLO ™ cement additive is a flow enhancer that is commerciallyavailable from Halliburton Energy Services, Duncan, Oklahoma.

For each of Test Nos. 4-9, a summary of the sample composition andthickening times at a T_(Test) of 575° F. is provided below in Table 2.The sample compositions utilized in Test Nos. 4-9 are comparative cementcompositions that comprise a conventional set retarder composition.TABLE 2 575° F. Tests TEST NO. Test Test Test Test Test Test No. 4 No. 5No. 6 No. 7¹ No. 8 No. 9 Class H 94 94 94 94 94 94 Cement (lbs/sack) %SSA-1 0 0 0 10 10 10 bwoc % SSA-2 35 40 0 30 30 30 bwoc Hi-Dense ® 68.870 0 0 0 0 No. 4 lbs/sk MicroMax ® 0 0 0 75 80 35 lbs/sk % NaCl 0 0 0 1855 18 bwow % SCR ™- 0 0 0 5 5 3 500 bwoc % HR ®-12 6 6 6 0 0 0 bwoc %HR ®-25 0 0 0 5 5 0 bwoc % COMPO- 6 3 6 0 0 3 NENT R ™ bwoc Micro 0 0 00 0 2 Matrix ™ Cement Retarder (gal/sk) % Gasstop ™ 0 0.8 0 0.8 0.8 0.8HT% bwoc % EZ-FLO ™ 0 0.07 0 0.07 0.07 0.07 bwoc % Diacel ® 0 1 0 0 0 0LWL bwoc² Water 6 6 4.15 6.51 6.79 2.85 (gal/sack) Density 19 19 16.2 1919 19 (lb/gal) Yield 1.79 1.84 1.15 1.98 2.18 1.25 (ft³/sack) Minutes 9090 90 90 90 90 to T_(Test) T_(Test) (° F.) 575 575 575 575 575 575Thickening 1:45 1:08 1:19 1:55 1:10 3:12³ Time (hr:min)¹The sample composition used in Test No. 7 was the same as the samplecomposition used in Test No. 3.²Diacel ® LWL Cement Fluid-Loss/Retarder Additive is a bi-functionaladditive that may be effective as both a fluid loss control additive anda set retarder composition. It is commercially available from ChevronPhilips Chemical Company LP, The Woodlands, Texas.³Test No. 9 was performed at 22,500 psi.

For each of Test Nos. 10-15, a summary of the sample composition andthickening times at a T_(Test) between 475° F. and 525° F. is providedbelow in Table 3. The sample compositions utilized in Test Nos. 10-15are cement compositions of the present invention that comprise aconventional set retarder composition and EDTA or NTA. TABLE 3 475° F.to 525° F. Tests TEST NO. Test Test Test Test Test Test No. 10¹ No. 11¹No. 12 No. 13 No. 14 No. 15 Class H 94 94 94 94 94 94 Cement (lbs/sack)% SSA-1 bwoc 10 10 10 10 10 10 % SSA-2 bwoc 30 30 30 30 30 30 MicroMax ®90 90 75 90 90 90 lbs/sk % NaCl bwow 18 18 18 18 18 18 % EDTA bwoc 0 02.4 6 5 5 % NTA bwoc 6 6 0 0 0 0 % SCR ™-500 5 5 0 5 0 5 bwoc % HR-25bwoc 5 5 5 5 5 5 % CFR ™-3 0 0 0 2 0 0 bwoc % CFR ™-1 0 0 0 0 0 0 bwoc %Gasstop ™ 0 0 0 0.8 0 0.8 HT bwoc % EZ-FLO ™ 0.07 0.07 0.07 0.07 0.070.07 bwoc Water 7.37 7.37 6.56 7.3 7.39 7.36 (gal/sack) Density 19 19 1919 18 19 (lb/gal) Yield 2.18 2.18 1.99 2.18 2.17 2.17 (ft³/sack) Minutes90 90 90 100 90 100 to T_(Test) T_(Test) (° F.) 475° F. 500° F. 500 500500 525 Thickening 6:00+² 6:00+² 1:28 4:45 8:00+² 3:58 Time (hr:min)¹Tests No. 10 and No. 11 were performed at 27,000 psi.²For Test Nos. 10, 11, and 14, the heat was turned off at the indicatedtime and cooled overnight (about 12 hours). When the slurry cap wasopened, the sample was set hard.

For each of Test Nos. 16-19, a summary of the sample composition andthickening times at a T_(Test) between 550° F. and 575° F. is providedbelow in Table 4. The sample compositions utilized in Test Nos. 16-19are cement compositions of the present invention that comprise aconventional set retarder composition and acid, wherein the acidcomprises EDTA, NTA, or a combination thereof. TABLE 4 550° F. to 575°F. Tests TEST NO. Test Test Test Test No. 16¹ No. 17 No. 18 No. 19²Class H Cement (lbs/sack) 94 94 94 94 % SSA-1 bwoc 10 10 10 25 % SSA-2bwoc 30 30 30 30 MicroMax ® lbs/sk 90 90 90 90 % NaCl bwow 18 18 18 18 %EDTA bwoc 0 6 5 5 % NTA bwoc 6 0 1 0 % SCR ™-500 bwoc 5 5 0 0 % HR ®-25bwoc 5 5 5 5 % COMPONENT R ® bwoc 0 0 0 0 % CFR ™-3 bwoc 0 2.5 0 0 %Gasstop ™ HT bwoc 0 0.8 0.8 0 % EZ-FLO ™ bwoc 0.07 0.07 0.07 0.07 Water(gal/sack) 7.37 7.2 7.37 7.39 Density (lb/gal) 19 19 19 18 Yield(ft³/sack) 2.18 2.18 2.18 2.17 Minutes to T_(Test) 100 100 100 90T_(Test) (° F.) 550 550 550 575 Thickening Time (hr:min) 1:37 1:46 1:461:52¹The sample composition used in Test No. 16 was the same as the samplecompositions used in Test Nos 10 and 11.²The sample composition used in Test No. 19 was the same as the samplecomposition used in Test No. 14.

For each of Test Nos. 20-23, a summary of the sample composition andthickening times at a T_(Test) of 575° F. is provided below in Table 5.Test Nos. 20 and 22-23 are cement compositions of the present inventionthat comprise a conventional set retarder composition, EDTA, and a SSMAcopolymer. Sample No. 21 is a cement composition of the presentinvention that comprises a conventional set retarder composition, NTA,and a SSMA copolymer. TABLE 5 575° F. Tests TEST NO. Test Test Test TestNo. 20 No. 21 No. 22 No. 23 Class H Cement (lbs/sack) 94 94 94 94 %SSA-1 bwoc 10 10 10 10 % SSA-2 bwoc 30 30 30 30 Hi-Dense ® No. 4 lbs/sk65 65 65 65 % NaCl bwow 18 18 18 18 % Narlex ® D-72 bwoc 4 4 5 5 % EDTAbwoc 1 0 5 5 % NTA bwoc 0 1 0 0 % HR ®-25 bwoc 5 5 0 5 % CFR ™-3 bwoc 40 0 0 % EZ-FLO bwoc 0.07 0.07 0.07 0.07 Water (gal/sack) 6.03 6.08 6.226.09 Density (lb/gal) 19 19 19 19 Yield (ft³/sack) 1.84 1.84 1.85 1.88Minutes to T_(Test) 199 90 90 90 T_(Test) (° F.) 575 575 575 575Thickening Time (hr:min) 4:00 3:25 2:24 3:01

Therefore, this example indicates, among other things, that the use ofcement compositions of the present invention, that comprise water, acement, a strength-retrogression additive, a conventional set retardercomposition, and an acid, wherein the acid comprises EDTA, NTA, or acombination thereof, may provide a desirable level of set retardation.

Therefore, the present invention is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as thosethat are inherent therein. While numerous changes may be made by thoseskilled in the art, such changes are encompassed within the spirit ofthis invention as defined by the appended claims.

1. A cement composition comprising: water, a cement, astrength-retrogression additive, and a set retarder compositioncomprising an acid selected from the group consisting of:ethylenediamine tetra acetic acid, nitrilotriacetic acid, andcombinations thereof.
 2. The cement composition of claim 1 wherein thestrength retrogression agent comprises a silica.
 3. The cementcomposition of claim 1 wherein the cement composition further comprisesan additional set retarder composition.
 4. The cement composition ofclaim 1 wherein the cement composition further comprises an additionalset retarder composition selected from the group consisting of: alignosulfate, a hydroxycarboxy acid, a phosphonic acid derivative, aborate salt, a synthetic polymer, and combinations thereof.
 5. Thecement composition of claim 1 wherein the cement composition comprisesthe ethylenediamine tetra acetic acid in an amount in the range of fromabout 0.01% to about 10% by weight of the cement.
 6. The cementcomposition of claim 1 wherein the cement composition comprises thenitrilotriacetic acid in an amount in the range of from about 0.01% toabout 10% by weight of the cement.
 7. The cement composition of claim 1wherein the cement composition comprises the ethylenediamine tetraacetic acid and the nitrilotriacetic acid in an ethylenediamine tetraacetic acid to nitrilotriacetic acid weight ratio in the range of fromabout 1:5 by weight to about 5:1 by weight.
 8. The cement composition ofclaim 1 wherein the cement composition further comprises a copolymercomprising olefinically unsaturated non-acrylate sulfonate monomers andolefinically unsaturated carboxylic acid monomers.
 9. The cementcomposition of claim 1 wherein the cement composition further comprisesa styrene sulfonic acid and maleic anhydride copolymer.
 10. The cementcomposition of claim 1 wherein the cement composition further comprisesa dispersant.
 11. A cement composition comprising: water, a cement, astrength-retrogression additive, and a set retarder compositioncomprising ethylenediamine tetra acetic acid.
 12. The cement compositionof claim 11 wherein the cement composition further comprises anadditional set retarder composition.
 13. The cement composition of claim11 wherein the cement composition further comprises a copolymercomprising olefinically unsaturated non-acrylate sulfonate monomers andolefinically unsaturated carboxylic acid monomers.
 14. A cementcomposition comprising: water, a cement, a strength-retrogressionadditive, and a set retarder composition comprising nitrilotriaceticacid.
 15. The cement composition of claim 14 wherein the cementcomposition further comprises an additional set retarder composition.16. The cement composition of claim 14 wherein the cement compositionfurther comprises a copolymer comprising olefinically unsaturatednon-acrylate sulfonate monomers and olefinically unsaturated carboxylicacid monomers.
 17. A set retarder composition comprising an acidselected from the group consisting of ethylenediamine tetra acetic acid,nitrilotriacetic acid, and combinations thereof.
 18. The set retardercomposition of claim 17 further comprising an additional set retardercomposition.
 19. The set retarder composition of claim 17 wherein theadditional set retarder composition is selected from the groupconsisting of: a lignosulfate, a hydroxycarboxy acid, a phosphonic acidderivative, a borate salt, a synthetic polymer, and combinationsthereof.
 20. The set retarder composition of claim 17 wherein the setretarder composition further comprises a copolymer comprisingolefinically unsaturated non-acrylate sulfonate monomers andolefinically unsaturated carboxylic acid monomers.